1. Field of the Invention
The invention relates to a receiver having a signal path incorporating a tuner, a demodulator circuit for supplying a stereo multiplex signal comprising a baseband stereo sum signal (L+R), a 19 kHz stereo pilot and a stereo difference signal (L-R) which is double sideband amplitude-modulated on a suppressed 38 kHz subcarrier, a sampler for converting an analog signal into a time-discrete signal and a stereo decoder for time-division multiplex decoding of a time-discrete stereo multiplex signal into time-discrete left and right stereo signals.
2. Description of the Related Art
A receiver of this type is known per se, for example, from the article "Digital Signal Processing type Stereo FM Receiver" by M. Hagiwara et al., published in IEEE Transactions on Consumer Electronics, Vol. CE-32, No. 1, February 1986, pp. 37-43.
In the known receiver a desired RF-FM reception signal is converted into an FM-IF signal by means of the tuner. This FM-IF signal is demodulated in the demodulator circuit. When being tuned to an FM stereo transmitter, the desired baseband modulation signal thus obtained comprises a stereo multiplex signal. Such a baseband stereo multiplex signal comprises a stereo sum signal (L+R) between 0 and 15 kHz, a stereo pilot at 19 kHz and a stereo difference signal (L-R) which is double sideband amplitude-modulated on a suppressed 38 kHz subcarrier. In the known receiver this baseband modulation signal and hence the stereo multiplex signal are applied in a digitized form (i.e. time and amplitude-discrete) to the stereo decoder which decodes the digital stereo multiplex signal into left and right stereo signals L and R. The sampler, which may be arranged, for example, upstream or downstream of the demodulator circuit or which may be incorporated in the demodulator circuit is, used for the digitization.
However, outside the frequency range of the stereo multiplex signal, the baseband modulation signal, may also comprise additional information such as, for example, radio data signals (RDS) and/or traffic transmitter identification (ARI) signals which are modulated on a 57 kHz RDS carrier. In practice it appears to be necessary to filter the digital stereo multiplex signal before decoding this signal, inter alia to prevent aliasing of these additional signals. Due to the comparatively small frequency space between the highest frequency in the stereo multiplex signal and the frequency range around said 57 kHz RDS carrier required for said additional information, stringent selectivity requirements are imposed on the filters for selecting the stereo multiplex signal. Such filters are complex and difficult to integrate, which makes them comparatively expensive.